1. Field of the Invention
The invention is in the field of fluidic bearing dry piston seals which enclose a working fluid reservoir between the piston seals and the cylinder wall in which inlet port and check valve means accessible to the working volume equalize the pressure on both sides of the seal bearings during the compression stroke and release the reservoir pressure during the expansion stroke.
2. Description of the Prior Art
The use of lubricated seals in some operations of compressors, such as in compressors used in cryogenic operations, have the problem of working fluid leakage from the working space in the cylinder and egress of the oil lubricants in the piston drive area into the working space. Leakage of oil into the engine cylinder is detrimental to good operation since eventually it goes into suspension as fine droplets in the working fluid and is thereupon filtered out by the finely divided metallic matrix of the regenerator. This partial blockage of the matrix pore space increases the pressure drop through the regenerator which reduces the power output of the engine. The temperature of the hot parts then increases because less heat is absorbed in expansion. Perhaps increased fuel may be supplied to compensate for the reduced power which further increases the temperature of the hot parts. The increase in temperature causes the oil trapped in the regenerator to carbonize which further increases the pressure drop. This progressive and cumulative deterioration in performance continues until eventually the engine becomes overheated and either the heater tubes or the regenerator matrix burn out.
It is tempting to avoid these problems using pre-packed sealed grease lubricated bearings, to use Oilite phosphor bronze oil impregnated bearings, or the many proprietary Teflon or Rulon bearings. These approaches are acceptable for experimental or prototype engines for short operating periods. However, for long term operation none of these approaches proved satisfactory, and it is likely that lubricating oil will continue to be used for the bearings in the crank mechanism. In that case, the problem of preventing egress of oil to the working space will need to be confronted and will likely be a difficult problem to overcome.
Carbonaceous materials, frequently impregnated with bronze, silver, or other metal powders are used as oil free bearing materials in many applications. Unfortunately, carbon loses its favorable lubrication properties in very dry atmospheres. Little published data is known about the use of carbon-based materials as bearings with hydrogen or helium working fluids at high pressure. Attempts to incorporate carbon-based materials in the seals and bearings of small cooling engines have not been found to be feasible.